This program's objective is to develop a new technology: x-ray detectors based upon silicon drift chamber (SDC) detectors specifically designed for optimal performance in the 500 eV to 10 keV region that will provide orders of magnitude advancement in energy dispersive x-ray detectors for biomedical research at Synchrotron Radiation (SR) research facilities. The proposed SDC detectors will be capable of attaining electronic noise below 10 e rms at peaking times as fast as 90 ns and will allow throughput rates of over 106 cps, and will not require cryogenic cooling. The predicted increases in count rate capability will allow x-ray absorption spectroscopy (XAS) research at ultra-low dilutions (or as a function of time, temperature, or concentration) that would otherwise be unfeasible or even impossible. Used with high brightness wigglers and undulators on both existing and next generation SR sources, these detectors will enhance the capability of obtaining the direct structural, bonding and compositional information which has been found to be so important in unravelling the mechanisms of protein and enzyme function at the molecular level. The proposed effort is based upon and relies upon the experience gained in our previous work developing advanced HgI2 array detectors for XAS as well as on utilization of sub-component technology already developed in this previous work. The detector development program now proposed has specific goals which are divided into two technical phases: (Phase l) Study optimal structures and develop prototypes of special detector structures leading to the targeted performance goals in terms of low noise, high efficiency, and high count rate for x-rays, and 2) Evaluate prototype detectors on the x-ray beam-lines at SSRL using standard spectroscopy electronics. Second, (Phase 2): a) Develop finalized SDC structures based upon the Phase l studies, b) Design and develop integrated input transistor-preamplifier structure required in order to utilize the drift detectors small capacitance and achieve the desired low noise and high rates, c) Develop a specialized housing for the integrated detector/EET, d) Develop specialized electronics as necessary to achieve optimal performance from SDC detectors and e) Construct and deploy a detector at the Stanford Synchrotron Radiation Laboratory (SSRL).